Why does the estimate avg. CPC changes when we change the location? I'm talking about adword?

Try selecting 'all regions' to see what you would get and then try US and your own country too and see the outcome too...that would give you a better understanding of how it works and what works. I hope this answered your question?

Well I am no expert on this but I'm from the UK and always select US when chosing keywords as this is were most of the traffic comes from for most keywords.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.